So far, for example, as disclosed in Japanese Patent Laid-Open No. 2004-184331, there has been an object recognition apparatus designed to emit an optical wave such as a laser beam to detect a reflected wave for recognizing an object existing in a forward direction. Such an apparatus is, for example, applicable to an apparatus made to detect a vehicle in a forward direction and issue an alarm, an apparatus made to control a vehicle speed for keeping a predetermined distance (inter-vehicle distance) between a subject vehicle and the vehicle ahead, or the like. That is, it has been incorporated into applications involving the recognition of a vehicle existing a forward direction.
The aforesaid object recognition apparatus is designed to emit a plurality of transmission waves (laser beams) forwardly toward a target in a predetermined position relative to the subject vehicle, and to determine a laser beam having a strongest intensity among the reflected laser beams in each of horizontal (X axis) and vertical (Y axis) directions. The laser beams having the strongest intensity is used as the center of X axis and Y axis of a recognition area used for recognizing an object in front of the subject vehicle. That is, the recognition area is defined as an area within a predetermined angle relative to the center of X axis and Y axis.
The object recognition apparatus uses the recognition area defined in the above-described manner for scanning the object in order to have a greater disposition tolerance angle when the apparatus is disposed on the subject vehicle. In this manner, the object recognition apparatus can emit the laser beam in an appropriate direction for recognizing the object in front of the subject vehicle.
In addition, the object recognition apparatus determines a vertical axis adjustment angle based on the intensity of the two laser beams that sandwiches a strongest laser beam defined as the center of the Y axis in the above-described manner. That is, the vertical axis adjustment angle is a deviation angle of an axis of the center laser beam from a reference angle in the vertical (Y axis) direction. The axis of the center laser beam may deviate from a direction defined by the reference angle because of the relatively wide angle of the laser beam in the vertical (Y axis) direction. The vertical axis adjustment angle is used to determine whether the radar unit of the object recognition apparatus is disposed in an upwardly deviated manner, or in a downwardly deviated manner relative to the reference angle.
However, an actual range of angle of the laser beam, that is, the angle of the axis of the center laser beam is affected by various factors even when the recognition area and the vertical axis adjustment angle are determined in the above-described manner. For example, the actual range of angle of the laser beam radiated from the radar unit may be diverted from the recognition area especially in the vertical (Y axis) direction when the subject vehicle has a heavy load and/or occupants loaded therein.
In this case, the object recognition apparatus disclosed in Japanese Patent Laid-Open No. 2004-184331 uses a reflector disposed on a back surface of a vehicle to have a reflected laser beam for detecting the deviation angle (the vertical axis adjustment angle) of the axis of the laser beam from the reference angle. The deviation angle, i.e., the vertical axis adjustment angle is used to adjust a disposition angle of the radar unit. In this manner, the direction of the laser beam radiated from the radar unit is accurately determined whether it is deviated upward or downward from the reference angle.
The height of the reflector on the back surface of a vehicle varies according to a type of the vehicle, and the height of the reflector greatly differs between a passenger type vehicle and a truck type vehicle. The object recognition apparatus described above is designed to detect the deviation angle from the reference angle only by using the reflected laser beam from the passenger type vehicle because the variation of the reflector height among passenger type vehicles is relatively small. That is, the deviation angle is determined only by using the reflected laser beam from a vehicle that is determined as the passenger type vehicle based on the width of the vehicle.
The deviation angle can accurately be calculated and determined in the above-described manner at the sacrifice of occasions for determining the deviation angle by using the reflected laser beam from the truck type vehicle. In other words, change in the deviation angle because of the heavy load and/or occupants cannot be detected while, for example, the subject vehicle is traveling behind the truck type vehicle.